Drawing FIG. 1 is a sectional elevational view of a conventional power-transmission sheave (8) that includes a centrally-open (11) hub portion 10 surrounding a directionally transversely extending hub-axis 9 that is surroundably engageable with a shaft 7 (depicted in phantom line). In the latter regard, hub portion 10 is provided with a threaded aperture 12 to accommodate a set-screw 6 (depicted in phantom line) for engaging the herein keyed shaft 7. In addition to hub portion 10, conventional sheave 8 includes at least one grooved (21) belt-training portion 20 and which groove 21 (at its base 22) circularly concentrically surrounds hub-axis 9 whereby belt-training portion 20 provides the sheave outward periphery 29. The at least one belt-training groove 21 is sidewardly defined by transversely separated flanged sides 30 and 40, the latter being sometimes divergent to provide the "V"-shaped groove depicted in FIG. 1. Power-transmission belt 5 (depicted in phantom line) is trained about and is co-rotatable with shaft 7 and sheave 8. In such co-rotatable condition, the belt lower portion (i.e. that adjacent groove base 22) is in compression and belt upper portion (i.e. that remote from groove base 22) is in tension. An elevational view of conventional sheave 8 and taken along line 1A--1A would be substantially identical to FIG. 3, except lacking openings 31 and 41.